X-band electron spin resonance (ESR) spectroscopy has been performed for gold nanorods (AuNRs) of four different sizes covered with a diamagnetic stabilizing component, cetyltrimethylammmonium bromide. The ESR spectra show ferromagnetic features such
as hysteresis and resonance field shift, depending on the size of the AuNRs. In addition, the ferromagnetic transition is indicated by an abrupt change in the spectra of the two smallest AuNRs studied. A large g-value in the paramagnetic region suggests that the ferromagnetism in the AuNRs originates from strong spin-orbit interaction.
We have measured the specific heat of the S = 1/2 alternating Heisenberg antiferromagnetic chain compound pentafluorophenyl nitronyl nitroxide in magnetic fields using a single crystal and powder. A sharp peak due to field-induced magnetic ordering (
FIMO) is observed in both samples. The H-T phase boundary of the FIMO of the single crystal is symmetric with respect to the central field of the gapless field region HC1 < H < HC2, whereas it is distorted for the powder whose ordering temperatures are lower. An analysis employing calculations based on the finite temperature density matrix renormalization group indicates the possibility of novel incommensurate ordering due to frustration in the powder around the central field.
